Despite its importance to the continuation of species, the differentiation of primordial germ cells into functional oocytes is poorly understood. Primordial germ cells begin to differentiate into oocytes during embryonic development in the mouse. Prior to birth, the oocytes develop in clusters called germline cysts, a conserved phase of oocyte development in both vertebrates and invertebrates. During late fetal and early neonatal development, mouse germ cell cysts break apart into single oocytes that become surrounded by pre-granulosa cells to form primordial follicles. During this process of cyst breakdown, a subset of cells in each cyst die with only a third of the initial number of oocytes surviving to form primordial follicles. The mechanisms that control cyst breakdown, oocyte apoptosis and follicle assembly are currently unknown. The long-term goal is to understand molecular and cellular mechanisms that regulate cyst breakdown and programmed cell death to establish the primordial follicle pool in the mouse ovary. The objective of this proposal is to determine the role of two pathways, the KIT signaling pathway and the BCL2 apoptotic pathway in modulating cyst breakdown and oocyte numbers. The central hypothesis of the proposed research is that cyst breakdown and germ cell death are controlled by signaling through the receptor tyrosine kinase, KIT and by a balance of BCL2 pro- and anti-apoptotic proteins. Recent work from our laboratory suggests KIT signaling may play an important role. In addition, we provide preliminary data demonstrating that BCL2 family proteins are also important for the regulation of cyst breakdown and associated programmed cell death. This proposal explores the molecular and cellular aspects of KIT signaling and programmed cell death regulators in cyst breakdown and oocyte survival. The specific aims of this research are to: 1) elucidate the molecular and cellular mechanisms of KIT signaling in cyst breakdown and associated oocyte loss; and 2) identify BCL2 family members involved in regulating oocyte survival. These goals will be achieved through techniques including immunocytochemistry, confocal microscopy, Western blotting, ovary organ culture, pharmacological inhibitors, siRNA technology and genetics. Research proposed in the current application is significant because it will enhance our current knowledge by elucidating the mechanisms by which cyst breakdown and associated oocyte loss are regulated. Results obtained in this grant will help improve research efforts in ovarian biology and in treatment of conditions causing female infertility such as primary ovarian insufficiency.